I ran into this on a local install of MediaWiki. With the default setting (in
1.3.1 anyway) of $wgUseImageResize = false, including image options like this:
[[Image:some_image.jpg|frame|center|Some caption]]
will not work. The problem is in makeImageLinkObj() in Skin.php: options are
not processed unless $wgUseImageResize == true, despite the fact that only the
thumb and __px options are related to image resizing.
The workaround is of course to set $wgUseImageResize = true in
LocalSettings.php, but it's not very intuitive that the way to enable image
alignment and framing is to set a resize flag.

Ah, I thought I might be missing something. Is there any reason not to just
always enable the extended image syntax? We could just put checks on
$wgUseImageResize round bits of code that actually do image resizing. This could
also allow us to have the fallback ability somebody asked for of setting height=
and width= attributes on the image without actually generating a thumbnail.